1. Field of the Invention
The present invention relates to an interchangeable lens digital camera.
2. Description Related to the Prior Art
As an image sensor mounted in a digital camera, a CMOS (complementary metal oxide semiconductor) type image sensor is known. Compared to CCD image sensors, CMOS type image sensors (hereinafter referred to as CMOS sensors) have conventionally been more affected by noises and inferior in image quality. However, recent various improvements provide CMOS sensors with higher image quality enough for employing the CMOS sensors in interchangeable lens digital cameras which are generally used for acquisition of high-quality images. An interchangeable lens digital camera consists of a camera body and interchangeable lenses which are each detachably attachable to the camera body, enabling an imaging with one interchangeable lens that accords with the purpose of the imaging. These interchangeable lens digital cameras include those called a single-lens reflex camera and a mirror-less single-lens reflex camera.
The CMOS sensor has a plurality of pixels (photodiodes) arranged in a two dimensional array, each pixel accumulating signal charges according to the exposure amount thereof. Each pixel of the CMOS sensor starts accumulating the signal charges right after being reset. The signal charges accumulated in the pixels are read out after the elapse of a predetermined exposure time, and are converted to voltages to be output as a pixel signal. As an exposure method for the CMOS sensor having this configuration, a rolling shutter method is employed. According to the rolling shutter method, a sequence of operations consisting of resetting and exposing the pixels and reading out the pixel signal are executed sequentially from one scanning line to another at the timing shifted from each other, the scanning line being a line of pixels aligned in the horizontal direction. The timing of each sequence may be shifted from pixel to pixel or in the unit of a number of scanning lines.
The abovementioned rolling shutter method enables high-speed successive imaging and contributes to reducing power consumption. However, because of the difference in exposure timing between the pixels or between the scanning lines, the image captured according to the rolling shutter method may have a distortion called rolling shutter distortion if the digital camera sways during the imaging due to camera shake, panning or the like, or if the subject moves during the imaging.
JPA No. 2012-080490 and JPA No. 2011-103631 disclose digital cameras which are provided with a capability of correcting the rolling shutter distortion. The digital camera in JPA No. 2012-080490 is provided with a CMOS sensor, an image data processor consisting of a calculator section calculating the displacement of a subject image between adjacent scanning lines, and a corrector section correcting the rolling shutter distortion on the basis of the calculation result. The calculator section divides each scanning line into multiple blocks and obtains the degree of correlation between the image signals from one block of one scanning line and another block of the adjacent scanning line. On the basis of the correlation degree, the calculator section detects a subject image that is moving relatively to an imaging plane of the CMOS sensor, and calculates the displacement of the subject image. The corrector section corrects the rolling shutter distortion by moving the detected subject image in accordance with the displacement between the scanning lines.
The digital camera disclosed in JPA No. 2011-103631 is provided with a shake compensation device consisting of a shake detection sensor which detects the camera shake and the panning, and a shake compensating section which moves the image sensor or a compensation lens on the basis of the detection result obtained by the shake detection sensor. When the shake detection sensor detects the camera shake, the shake compensating section makes an operation to compensate for the camera shake. When the shake detection sensor detects the panning, the shake compensating section makes a compensative operation for correcting the rolling shutter distortion. Note that the panning is an operation of turning the camera in the horizontal direction, for example, for the purpose of tracking and shooting a moving subject.
Some digital cameras have a capability of displaying images taken through an image sensor sequentially on an image display unit, i.e., so-called the live view function. The image displayed on the image display unit by means of this live view function (hereinafter referred to as the live view image) are used for checking the view angle and the composition. The digital camera loaded with a CMOS sensor has a problem that the rolling shutter distortion occurs also in the live view image and bothers the photographer.
The image data processor described in JPA No. 2012-080490 is capable of correcting the rolling shutter distortion of the live view image as well. However, as described above, since the image data processor in JPA No. 2012-080490 calculates the shift amounts of a subject image between the adjacent scanning lines, as the subject image is moving relatively to the imaging plane of the CMOS sensor, there will be a time lag in displaying the live view image if it takes much time for this calculation. Considering the abovementioned application of the live view image, such a display time lag of the live view image is not preferable. Meanwhile, the method of moving the image sensor or the compensation lens on the basis of the detection result from the shake detection sensor, as employed in the shake compensation device in JPA No. 2011-103631, would not cause such a display time lag of the live view image because the shake compensation has been executed at the time of imaging through the CMOS sensor. However, the shake compensation method by moving the image sensor or the compensation lens is merely effective for correcting a blur due to instability of the camera such as camera shake, but not suitable for correcting a picture deviation caused by a large motion such as the panning of the camera.
Therefore, it is preferable to correct the rolling shutter distortion of the live view image in the manner as described in JPA No. 2012-080490, by means of an image data processor on the basis of the detection result from a shake detection sensor. However, in some kinds of interchangeable lens digital cameras, in which CMOS sensors are increasingly employed, a shake detection sensor and a shake compensation device including a compensation lens are integrated in the interchangeable lens so as to perform the shake compensation by the interchangeable lens independently. In these kinds of interchangeable lens digital cameras, the detection result from the shake detection sensor is not transmitted from the interchangeable lens to the camera body for the sake of correcting the rolling shutter distortion. Because a CMOS sensor and an image data processor are built in the camera body, it is impossible to correct the rolling shutter distortion of the live view image on the camera body side on the basis of the detection result from the shake detection sensor of the interchangeable lens.